This invention relates of a method and apparatus for treating any material such as water with a gas containing ozone. The apparatus may be used in the production of water suitable for human consumption from water contaminated by one or more of microorganisms, chemicals, heavy metals and minerals.
Generally, drinking water is produced by municipalities from a lake or ground water by treating the water with ozone or chlorine. Once the water is treated, it is transported to households by pipes. Over time, contaminants may infiltrate into the pipeline. Accordingly, even though the potable drinking water is fed into the pipeline from a water treatment facility, the water may be contaminated by the time it enters a residence. Further, if there is a breakdown in equipment at the water treatment facility or a flood, contaminated water may enter the pipeline.
A variety of domestic filtration systems have been developed for use by consumers to filter water that is delivered by a tap. Such systems may use a filter made from a combination of a porous media filter and activated carbon through which water is passed. This type of system will reduce the levels of chlorine, lead, and pesticides. However, there are several disadvantages associated with this device. In particular, a filtration system will not remove microbiological contaminants from water.
Another popular system in use for the purification of contaminated water is a system which employs ultraviolet light for disinfection in series with a porous media and carbon filter. This type of system will reduce the levels of chlorine, lead, and pesticides and has some disinfection capability. One disadvantage with this system is that the ultraviolet light""s disinfection efficacy is greatly diminished by turbidity or colour in the water which can cause the filter to become contaminated by microorganisms which can readily live and breed therein thereby multiplying the danger from any microorganisms which may be present. Thus, the filter of this system also suffers from the disadvantages associated with filters of filtration based systems.
Water treatment apparatus using oxidizing gases have been developed. Some of these devices operate on a batch basis. According to this process, the water is placed in a treatment container and the treatment agent (e.g. a gas), is dispersed through the water, such as via a sparger. Following the completion of the cycle, the water may then be used. One disadvantage with small scale ozone treatment systems such as for domestic applications is to produce an effective amount of ozone to kill a variety of different microbiological agents that may be present in the water.
One method that has been used to generate ozone is corona discharge. Producing corona discharge in a gap through which an oxygen bearing gas is passed can be used to produce ozone. One disadvantage of this approach is that the thermodynamics limit the efficiency of the corona discharge method to produce ozone. The corona discharge results in the production of heat. Increases in the temperature of the ozone containing gas causes exponential increases in the rate of decomposition of ozone to oxygen. Therefore, if the heat is not dissipated, then the quantity and concentration of ozone produced and the thermodynamic efficiency of the ozone generator decreases.
Traditionally, the heat dissipation problem has been addressed by adding complex mechanical structures (e.g. heat sinks that may be air or water cooled, refrigeration) to reduce the steady state operating temperature of an ozone generator to improve ozone production. Disadvantage of this approach are cost and reliability of the ozone generator. The mechanical structure to dissipate heat adds complexity to the design of an ozone generator and increases the cost of the generator and the likelihood that the generator may fail in use. A further disadvantage is that the effectiveness of the cooling of the unit is limited by the rate of conduction and/or convection which is inherent in the design of the ozone generator. For example, if the cooling is applied to the outer housing of the ozone generator, then the limit of the effectiveness of the cooling is predicated upon the rate at which heat is transmitted from its point of production, the corona discharge gap, to the point of extraction (e.g. the outer housing). Further, some elements of an ozone generator are more problematic to cool, such as the high voltage electrode, due to the requirement that it be electrically insulated from the ground electrode and the user.
One method for cooling an ozone generator comprises passing a gas containing oxygen (eg. air) through a corona discharge field. The passage of the gas through the field causes oxygen molecules to recombine to produce ozone upon exposure to the corona discharge. Periodically, the corona discharge is de-energized. The period during which the ozone generator is de-energized may be constant or may be of variable length. During the de-energized periods, the air flow continues and the air flow is then used to directly cool the internal components of the ozone generator. This permits relatively rapid cooling of the ozone generator, without the added complexity of adding a heat exchanger. At the end of the period, the corona discharge is re-energized and ozone is again produced. The duty cycle (i.e. the time period during which the ozone generator is energized to produce a corona discharge) may only be reduced by, say 10 or 15%. However, as the rate of ozone decomposition to air is exponential, a corona discharge ozone generator operated in such a manner produces more grams and a higher concentration of ozone over a water treatment cycle than if the ozone generator were operated continuously for the entire water treatment cycle.
Therefore, in accordance with the instant invention, there is provided a method for treating a liquid with a gas containing ozone comprising the steps of passing the gas through an corona discharge ozone generator to produce gas containing ozone and introducing the gas containing ozone into the liquid; and, periodically de-energizing the ozone generator and passing gas through the ozone generator.
In accordance with another embodiment of the instant invention, there is also provided a method for cooling a corona discharge ozone generator comprises passing a gas containing ozone through the corona discharge ozone generator and energizing the ozone generator to produce gas containing ozone; and, periodically de-energizing the ozone generator and passing gas through the ozone generator whereby the ozone generator is cooled.
In one embodiment, the gas which passes through the ozone generator when it is de-energized is introduced into the liquid.
In another embodiment, the flow rate of gas through the ozone generator is varied when the ozone generator is de-energized.
In another embodiment, the flow rate of gas through the ozone generator is decreased when the ozone generator is energized.
In another embodiment, the flow rate of gas through the ozone generator when the ozone generator is energized is about 50 to 85% lower than when the ozone generator is de-energized.
In another embodiment, the method further comprises providing a substantially constant current to the ozone generator.
In another embodiment, the ozone generator is energized for 50 to 95% of period of time during which the liquid is being treated.
In another embodiment, at least two ozone generators are provided and the method further comprises selectively energizing one or more ozone generator and flowing the gas to the ozone generators whereby, periodically, at least one ozone generator is de-energized and is cooled by the gas flow. Preferably, a higher proportion of the gas is directed to the one or more ozone generator which is de-energized.
In another embodiment, the liquid is water and the method further comprises introducing the water to be treated into a treatment vessel prior to introducing the gas into the liquid whereby potable water is produced by contacting the water with the gas.
In another embodiment, the method further comprises providing first and second gas flow sources wherein the first gas flow source has a lower flow rate than the second gas flow source and directing the first gas flow source to the one or more ozone generator which is energized.
In another embodiment, the method further comprises providing a single gas flow source at a first flow rate and reducing the flow rate of gas from the single gas flow source to the one or more ozone generator which is energized.